Java Stream API, Collect result into Map<code, concatenated string> from a List containing two separate lists

Here is the code which need to generate the output as follows using Stream API.

Input:

[Subgroup(id=1, names=[Name(languageCode=1, longName=ABD), Name(languageCode=2, longName=BD)], level=Level(names=[Names(languages=1, longName=1 1), Names(languages=2, longName=2 2)]))]

Output:

Map:{1=ABD~1 1, 2=BD~2 2}

Java-6: Code which generates the required output. but, we need to use Stream API and collect the output because the Sample input i am providing only single obj. Where in realtime i am having more than 50 objects. So, i need it in Advanced version of Java.

public class SubgroupProcessor {
	public static void main(String[] args) {
		List<Name> names = Arrays.asList(new Name(1, "ABD"), new Name(2, "BD"));
		List<Names> namesLevel = Arrays.asList(new Names(1, "1 1"), new Names(2, "2 2"));
		List<Subgroup> subgroups = Arrays.asList(new Subgroup(1, names, new Level(namesLevel)));
		System.out.println(subgroups);

		Map<Integer, String> map = new HashMap<>();
		for (Subgroup subgroup : subgroups) {
			List<Name> names2 = subgroup.getNames();
			List<Names> namesLevel2 = subgroup.getLevel().getNames();
			for (Name name : names2) {
				for (Names nameLevel : namesLevel2) {
					if (nameLevel.getLanguages() == name.getLanguageCode()) {
						map.put(name.getLanguageCode(), name.getLongName() + "~" + nameLevel.getLongName());
					}
				}
			}
		}
		System.out.println("Map:"+map);
	}
}

@Data @AllArgsConstructor
class Subgroup {
	private int id;
	private List<Name> names;
	private Level level;
}

@Data @AllArgsConstructor
class Name {
	private int languageCode;
	private String longName;
}

@Data @AllArgsConstructor
class Names {
	private int languages;
	private String longName;
}

@Data @AllArgsConstructor
class Level {
	private List<Names> names;
}

Tried Chat-GPT as well but generated the following code and its not working.

This code uses Java 8 streams to process the input list and produce the required output in the form of a map with language codes as keys and concatenated names as values.

Map<Integer, String> map = subgroups.stream()
	.flatMap(subgroup -> subgroup.getNames().stream()
			.filter(name -> getMatching(subgroup, name))
			.map(name -> Map.entry(name.getLanguageCode(), name.getLongName() + "~" + getLevelLongName(subgroup, name)))
	)
	.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
    

public static boolean getMatching(Subgroup sg, Name name) {
	return sg.getLevel().getNames().stream()
			.anyMatch(ln -> ln.getLanguages() == name.getLanguageCode());
}

private static String getLevelLongName(Subgroup subgroup, Name name) {
	return subgroup.getLevel().getNames().stream()
			.filter(levelName -> levelName.getLanguages() == name.getLanguageCode())
			.map(Names::getLongName)
			.findFirst()
			.orElse("");
}

You may try something like this instead:

Map<Integer, String> result = subgroups.stream()
.flatMap(subgroup -> 
subgroup.getNames().stream()
.map(name -> new AbstractMap.SimpleEntry<>(
name.getLanguageCode(), 
name.getLongName() + "~" + 
subgroup.getLevel().getNames().stream()
.filter(levelName -> levelName.getLanguages() == name.getLanguageCode())
.map(Names::getLongName)
.findFirst()
.orElse("")))
)
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));